The present invention relates to a heat recovery apparatus and to a heat recovery method.
The greenhouse effect caused by CO2 is recognized as a major cause of global warming phenomena. The warming adversely affects the global environment in a devastating way, causing serious results such as unusual weather, including heavy rainfall, flooding, and the like, sea-level rise due to disappearance of glaciers, and resultant submersion of islands. From such viewpoints, measures to reduce CO2 emissions have internationally become an important and urgent issue.
Carbon dioxide is generated in any type of human activity that involves combustion of fossil fuels.
Accordingly, the following methods have been implemented in power generation facilities such as thermal power plants using large amounts of fossil fuels (coal and the like): one in which combustion exhaust gas of a boiler is brought into contact with an amine-based CO2 absorbing liquid, and thus CO2 in the combustion exhaust gas is removed and recovered; and another in which the CO2 thus recovered is stored without being released to the atmosphere. For example, the recovered CO2 is compressed in a CO2 compressor, and it is then sent to a CO2 storage site via a pipeline.
As the processes of removing and recovering CO2 from combustion exhaust gas by use of the CO2 absorbing liquid as described above, there may be employed a process in which combustion exhaust gas and the CO2 absorbing liquid are brought into contact with each other in an adsorption tower, and a process in which the absorbing liquid having absorbed CO2 is heated in a regeneration tower, to release CO2, and simultaneously the absorbing liquid is regenerated and circulated back to the adsorption tower for reuse (Japanese Patent Application Publication No. Hei 10-202054).
Here, the CO2-containing gas from the regeneration tower is heated, and thus, it has a temperature at or around 85° C. The present inventors have hypothesized that efficient recovery of the heat can improve power generation efficiency by at least 0.5%. Moreover, the temperature of the CO2 gas is raised in a CO2 compressor at the time of CO2 compression. Hence, the present inventors have also considered that effective recovery of the heat can further improve power generation efficiency.
Specifically, a CO2 recovery apparatus for a thermal power plant using coal or the like consumes a large amount of steam and a large amount of electricity, and hence causes a large reduction in power generation output. In addition, the CO2 recovery apparatus itself generates a low level of but a large amount of heat as described above. Accordingly, the present inventors have considered that, in order to prevent reduction in power generation output as much as possible, it is important to increase the amount of the power generation by utilizing the amount of heat generated by the CO2 recovery apparatus.
In accordance with this thinking, the present inventors have tried a system having a configuration shown in FIG. 3 (This configuration is not known to the public and is novel over the conventional art).
In a heat recovery apparatus 200 according to this configuration, a boiler feedwater heater 202 is provided upstream of a regeneration tower condenser 204 as in the current situation, and boiler feedwater from a thermal power plant 206 is supplied to the boiler feedwater heater 202 for cooling regeneration-tower-exit CO2 gas. Then, a method is employed in which the boiler feedwater is heated simultaneously with this cooling, and the heated liquid is returned to the thermal power plant 206. Before returned to the power plant, the heated liquid is caused to pass through a feedwater heater of a CO2 compressor, is further heated in the feedwater heater, and is then returned. Thereby, the amount of heat recovered is increased.
Note that the cooled regeneration-tower-exit CO2 gas is recovered as a product CO2 through a regeneration tower reflux drum 208. Moreover, water is recovered by a regeneration tower reflux pump 210 through a bottom portion of the regeneration tower reflux drum 208, and is refluxed to the regeneration tower as reflux water.
However, it turned out that this trial configuration has the following drawbacks and hence is not economical.
(1) Since it is necessary to send a large amount of flow (the entire amount of the boiler feedwater) to the boiler feedwater heater 202 for the effective recovery of heat, considerable modifications of the thermal power plant 206 are necessary.
(2) In a CO2 recovery apparatus for a large-scale coal thermal power plant, the number of heat exchangers increases, and pipes and the like increase, bringing about a problem regarding space limitation. Therefore, it is difficult to install such a CO2 recovery apparatus in an ordinary thermal power plant.
(3) The greater the amount of heat the boiler feedwater recovers from tower top CO2 gas of a regeneration tower, the more economical it is. However, because of the limitation of layout, it is practically impossible under the current situation to install multiple shell and tube type heat exchangers as the boiler feedwater heater 202.
(4) Moreover, pressure loss on a CO2 gas side in the boiler feedwater heater 202 becomes excessively large. Suppose a case in which trouble occurs in the feedwater heater of a CO2 compressor when heat of compression of CO2 in the CO2 compressor is recovered. In such a case, since the pressure of the CO2 gas is higher than the pressure of the boiler feedwater, there is a concern that the CO2 leaks, and exerts a significant effect on the operation of the power plant.
The present inventors have further researched in order to effectively recover heat of the CO2-regeneration-tower-exit CO2 gas and to increase an output of a turbine in a thermal power plant without causing such problems.